1. Field of the Invention
The present invention is directed to door locking devices and, more particularly, to electromagnetically controlled door locks that are actuatable from remote locations throughout a building. Such locks, known generally as xe2x80x9celectric strikesxe2x80x9d, are commonly used to prevent the opening of an associated access obstructing member, such as a door, in hotels, offices, apartment buildings, storage cabinets and appliances. In a preferred embodiment the electric strike of the present invention employs a guard clip for deterring picking of the locking mechanism, a springless solenoid designed to prevent the build-up of residual magnetism which otherwise impairs a solenoid""s ability upon activation to release the locking mechanism, and a one piece face plate for mounting in a door jamb which serves to house the electric strike and guide the latch bolt associated with an access obstructing member into engagement with the latch bolt keeper of the electric strike.
2. Description of the Related Art
Electronically-operable door strikes installed in a door jamb to secure a door against opening are known in the art. Electric strikes typically provide a latch bolt keeper mounted on a pivot. The ability of the keeper to rotate on the pivot is electronically controlled. When the keeper is free to rotate to a latch bolt releasing position, the latch bolt associated with the access obstructing member is not retained in the door jamb and the access obstructing member can be opened. When the keeper is not free to rotate, that is, it is in its latch bolt securing position, the latch bolt is retained by the latch bolt keeper, thus securing the door.
Fundamentally, the function of an electric door strike is based on the fact that a retractable stop lever engages the latch bolt keeper and holds it in its latch bolt securing position. That is, the stop lever prevents the latch bolt keeper from rotating. The stop lever is sometimes held in its engaging position with the latch bolt keeper by a lock lever spring-urged into interlocking relationship with the stop lever. To permit the latch bolt keeper to rotate to its latch bolt releasing position, a solenoid is often employed. The solenoid is electronically energized, normally by means of a circuit completing switch remote from the door strike, and the lock lever is moved out of its locking engagement with the stop lever by the action of the solenoid plunger either pulling or pushing the lock lever. The stop lever, no longer being engaged by and being held in position by the lock lever, is incapable of resisting pivoting of the latch bolt keeper when force is applied to the keeper. The keeper is therefore able to be rotated and the door thus able to be opened.
One drawback of some of the electric strikes heretofore available is the ease with which they can be picked open and defeated by the insertion of a tool for unauthorized movement of the latch bolt keeper to a latch bolt releasing position. U.S. Pat. No. 3,638,984 to Davidson and U.S. Pat. No. 3,861,727 to Froerup et al. disclose a latch bolt keeper provided with a lateral edge projection arranged to occupy an overlapping position with respect to an edge of the strike plate and thus close the space between this edge and the adjacent face of the latch bolt keeper so as to provide against the insertion of a picking tool. U.S. Pat. No. 4,026,589 to Hanchett, Jr. also discloses a latch guard which precludes insertion of a tool. Finally, U.S. Pat. No. 4,056,277 to Gamus et al. discloses a plurality of pin-like protrusions positioned to form a barrier to prevent access by a tool to the ball and socket arrangement which serves to hold the latch keeper of that invention in place. Unlike the prior art electric strikes heretofore disclosed, the present invention utilizes a unique guard clip designed to prevent a tool from gaining access to the lock lever and further, by means of its fish hook-like configuration, to redirect any tool which is inserted into the electric strike away from the lock lever and the stop lever.
Another disadvantage of the electric strikes heretofore available is the undesirable build-up of residual magnetism within the solenoid or on the solenoid plunger. It is essential for proper operation of a solenoid that it lose its magnetic force once input electrical power to the solenoid is removed, thus allowing the solenoid plunger to return to its original position. Any magnetic field which remains when electrical power is removed is termed residual magnetism. The residual magnetism present in prior art electric strikes is occasioned by the frequent contact between two ferrous metal surfaces such as a ferrous metal solenoid plunger striking a ferrous metal lock lever during repeated energization and de-energization of the solenoid. Build-up of residual magnetism during repeated cycling of the solenoid results in the eventual failure of the solenoid""s ability to remotely disengage the lock lever and the stop lever so as to permit the latch bolt keeper to be rotated and the access obstructing member opened. In some electric strikes termed xe2x80x9cfail-safexe2x80x9d or xe2x80x9cpower to lockxe2x80x9d by those of skill in the art, the plunger is pulled into the solenoid body when energized. This action of the plunger pulls the spring-resistive lock lever into engagement with the stop lever, thus preventing the latch bolt keeper from pivoting from its latch bolt securing position to its lockset latch bolt releasing position. When the solenoid is de-energized, the spring-urged lock lever returns to its original position where it is disengaged from the stop lever, thus allowing the latch bolt keeper to be pivoted to its lockset latch bolt releasing position. Upon the build-up of residual magnetism along the plunger or solenoid body, however, the plunger can remain in contact with the lock lever or not fully exit the body of the solenoid, thus compromising the ability of the lock lever to disengage from the stop lever. In the operation of other electric strikes, termed xe2x80x9cfail-securexe2x80x9d by those of skill in the art, the plunger is pulled from its starting position into the body of the solenoid upon energization and this action releases the stop lever, thus permitting the latch bolt keeper to rotate. Upon de-energization the plunger exits the solenoid body by means of a spring and is returned to its starting position. Again, however, upon the build-up of residual magnetism along the plunger, the plunger may not be able to be completely returned to its starting position by the spring mechanism, thus compromising the solenoid""s ability to return the stop lever or lock lever to a position where the latch bolt keeper is prevented from rotating.
Yet an additional drawback of prior art electric strikes is the large amount of cutting into a door jamb which is necessary to install the strike and its associated face plate. The ANSI standard face plate measures 4xe2x85x9e inches in length by 1xc2xc inches in width. Typically, electric strike face plates also utilize an auxiliary ramp which measure 3xe2x85x9c inches in length, thus necessitating that a corresponding length of the door jamb be removed at a depth of about one-half inch or more to properly seat the face plate and auxiliary ramp into the jamb. This large amount of cutting requires more time and money to install than otherwise would be necessary with an electric strike and face plate arrangement that reduces the amount of door jamb cutting required for installation. A still further drawback of prior art electric strike face plates occurs in those installations where the electric strike is required to be installed in door jambs which measure 4 inches or wider and the door is to be center hung. In those instances the auxiliary ramp and face plate comprise two or more pieces, thus again requiring more time for installation than if a one-piece face plate and auxiliary ramp were provided.
For the foregoing reasons, there is a need for an electric strike which overcomes the hereto before described problem of residual magnetism associated with a frequently cycled or continuous duty solenoid plunger. There is a further need for an electric strike in which a tool cannot be used to pry away the lock lever from the stop lever permitting the latch bolt keeper to be rotated and the access obstructing member opened by a tampering intruder. There is yet a still further need for an electric strike and face plate which reduces the amount of door jamb cutting necessary for its installation.
It is thus an object of the present invention to provide an electronically-operable door strike which utilizes a solenoid which avoids the build-up of residual magnetism along the solenoid body or plunger which otherwise would render the electric strike inoperable.
It is a further object of the present invention to provide an electronically-operable door strike which embodies an improved guard to the insertion of a picking tool and which redirects a picking tool away from contacting the lock lever or the stop lever.
It is a still further object of the present invention to provide an electronically-operable door strike and one piece face plate with full lip and auxiliary ramp arrangement which reduces the amount of door jamb material which must be removed for installation of the face plate.
In accordance with the foregoing objects, an electronically-operable door strike which employs a guard clip for deterring picking of the locking mechanism, a springless solenoid designed to avoid the build-up of residual magnetism and a face plate which reduces the amount of door jamb cutting required for installation of the electric strike and face plate arrangement is disclosed. Briefly stated, the invention is practiced by utilizing a guard clip which protects the lock lever and the stop lever from tampering by a tool inserted into the door strike along an edge of the latch bolt keeper and which by virtue of its xe2x80x9cfish hookxe2x80x9d configuration redirects the tool away from the lock lever. In addition, to avoid the build-up of residual magnetism, a solenoid comprising a ferrous metal shell and front cap, a rear cap of non-ferrous material such as non-ferrous metal, and a ferrous metal plunger with a non-ferrous metal protuberance is provided. An air gap is maintained between the front cap and the plunger body during movement of the plunger to avoid the build-up of residual magnetism between the front cap and the plunger body. An additional air gap is provided between the plunger and a spool within which the plunger moves and around which a wire coil is wrapped inside of the solenoid shell. This additional air gap aids in the dissipation of heat generated when the wire coil of the solenoid is electronically-activated and the plunger is repeatedly cycled. Finally, the face plate associated with the electric strike is designed with a full lip and flange tongue arrangement which reduces the amount of the door jamb which must be removed for the installation of the electric strike and face plate in comparison with heretofore known electric strike and face plate arrangements.
Further objects, features, aspects and advantages will be readily apparent to those skilled in the art and a better understanding of the present invention may be had by reference to the following detailed description taken in connection with the following drawings.